French chemist who is best known for Le Chatelier's principle, which makes it possible to predict the effect a change of conditions (such as temperature, pressure, or concentration of reaction components) will have on a chemical reaction. His principle proved invaluable in the chemical industry for developing the most-efficient chemical processes.

Le Chatelier was the first of six children. Coming from a bourgeois Roman Catholic family, he had the benefit of a privileged education. He attended the Collège Rollin in Paris, from which he earned undergraduate degrees in 1867 and 1868, before enrolling at the École Polytechnique in 1869. The following year, he entered the mining engineer program at the École des Mines in Paris, from which he graduated in 1873. In 1876 Le Chatelier married Geneviève Nicolas; together they raised seven children, three boys and four girls.

After two years in the provinces as a mining engineer, Le Chatelier returned to the École des Mines as a chemistry lecturer in 1877. He had at his disposal a well-equipped laboratory that he put to good use the following year by contributing to the Firedamp Commission, which was concerned with the improvement of safety in mines. Under the direction of the French mineralogist Ernest-François Mallard, Le Chatelier conducted experiments on explosive materials and published his first works of scientific research. These studies led him to improvements in measuring high temperatures, based on the thermocouple principle. He perfected the coupling of pure platinum with a platinum- rhodium alloy that gave rise to the thermoelectric pyrometer, known as the “Le Chatelier.” He also adapted an optic pyrometer for industrial use.

During the same period, Le Chatelier was interested in hydraulic binding materials (e.g., lime, cement, and plaster), which became the subject of a scientific thesis presented at the Sorbonne in Paris in 1887. This work established him as a scientific expert in the field.

Le Chatelier's early work led to the experimental study of thermodynamics. In 1884 he enunciated a general principle that defined how systems in chemical equilibrium maintain their stability, stating that

In other words, equilibria tend to minimize changes imposed on their conditions. This became known as Le Chatelier's principle, and it led him to develop mathematical equations to describe systems in equilibrium. Le Chatelier later recognized that the American mathematician Josiah Willard Gibbs (Gibbs, J Willard) had partially provided this mathematical formalization between 1876 and 1878. Consequently, in 1899 Le Chatelier devoted a year to studying these issues, concluding with a translation of Gibb's original work about chemical equilibrium systems.

Le Chatelier's attention then turned to the question of how to apply the science of chemical thermodynamics to the development of industrial processes. He suggested increasing the output of industrial ammonia production by using low heat and high pressure, as indicated by his principle of chemical equilibrium. Similarly, his interest in industrial applications of chemistry led him to perfect the oxyacetylene torch, which achieves the extremely high temperatures required for welding and cutting metals.

Metallurgy was the other specialized field where thermodynamic theories were used with notable success. Le Chatelier introduced to France methods of analyzing alloys based on metallography, and he also contributed to the method of drawing phase diagrams (phase diagram). All these studies were conducted while teaching in scientific institutions in Paris, and in 1882 Le Chatelier was nominated as a lecturer in chemistry at the prestigious École Polytechnique. His ambition had always been to achieve a position as a professor there, but that title was denied him. The École des Mines, however, was more welcoming, and in 1887 he obtained a professorship in industrial chemistry and metallurgy. Le Chatelier remained at the École des Mines until his retirement. In 1897 he succeeded Paul Schutzenberger in his chair of mineral chemistry at the Collège de France, and he also succeeded the Nobelist Henri Moissan (Moissan, Henri) at the Sorbonne in 1907.

Le Chatelier's career was largely devoted to the development of a systematic approach to organizing the relationship between science and industrial production. His teaching was entirely concerned with what he called industrial science—the scientific study of industrial phenomena in order to maximize outputs. He successfully introduced his ideas about industrial science to the Société d'Encouragement pour l'Industrie Nationale as guidelines for research programs initiated by the institution. He was elected president of the society in 1903 and 1904. In 1904 he founded and edited the Revue de métallurgie, which became a medium for his ideas on industrial science. By providing his services as a consultant for private companies, Le Chatelier also contributed directly to industrial development.

In 1907 Le Chatelier was elected to the French Academy of Sciences (Sciences, Academy of). He devoted most of his time to directing his students' research work at the Sorbonne and the École des Mines. He sat as a scientific expert on a variety of governmental committees concerned with such issues as the manufacture of explosive materials and military equipment. During World War I, he contributed to the reorganization of shell production in munitions factories. He dedicated a large part of his last years to promoting the American engineer Frederick W. Taylor (Taylor, Frederick W.)'s theories about the scientific organization of work. Le Chatelier translated some parts of Taylor's writings, and he also published his own papers on the subject.